(a) Field of the invention
The present invention relates to an objective optical system for endoscopes.
(B) Description of the prior art
Optical systems for endoscopes, especially of flexible endoscopes, comprises an objective arranged at the distal end and an optical fiber bundle arranged in rear of the objective and such optical systems are arranged to observe an image of an object by transmitting it by the optical fiber bundle.
In case of such endoscope comprising the optical fiber bundle, however, loss in intensity of light occurs when the light is transmitted by the optical fiber bundle. The above-mentioned loss in intensity of light becomes the smallest when the light enters the optical fiber bundle vertically to the end face of the optical fiber bundle. However, in order to let the light from the object enter vertically to the end face of the optical fiber bundle and to arrange so that a favourable image can be obtained, it is necessary to use an objective of complicated lens configuration.